The present invention relates to a seat belt retractor with a load limiter and a locking mechanism. More particularly, the present invention relates to a retractor having a motorized load limiter and locking mechansim.
Conventionally, retractors have include a mechanical load limiter such as a torsion bar or the like for limiting the load applied on a shoulder or chest of an occupant of a motor vehicle. In these conventional retractors the mechanical type of load limiter does not allow for the threshold setting for load on the webbing to be altered. Typically, the threshold value for the amount of tensile load to be applied to the webbing is determined according to the model type of automobile. This threshold value is fixed and cannot be easily altered.
Therefore, it is desired to develop a novel retractor in which the threshold value for tensile load on the seat belt webbing is adjustable.
To achieve the aforementioned object, the present invention provides a motorized seat belt retractor having a load limiter for controlling the tensile load on a webbing withdrawn in the event of emergency. The load limiter utilizes force generated by rotation of the motor shaft to control the tensile load. This approach to a load limiter is novel and may include a high-voltage motor having improved motor current rising characteristics during starting of the motor.
According to the structure of the present invention, the force generated by the rotation of the shaft of the motor can be utilized as the tensile load for the load limiter. This configuration allows for the easy adjustment of the threshold value of the tensile load on the webbing and permits the threshold value to be set over a wider range of possible values.
The load limiter of the motorized seat belt retractor includes a rotational resistance generating means which generates a rotational resistance force in response to the rotation of the shaft of the motor. According to this structure, during rotation of the shaft of the motor a rotational resistance force is generated due to the inertial moment of the shaft, this rotational resistance force can be positively utilized to control the tensile load on the webbing.
In the aforementioned motorized seat belt retractor which includes a load limiter for controlling the tensile load on a webbing withdrawn due to forward movement of an occupant in the event of emergency, the load limiter includes a rotational resistance generating means which provides for the generation of a rotational resistance force by the motor when the motor is short circuited. According to this structure, the rotational resistance force generated by the motor when short circuited can be positively utilized as the tensile load for the load limiter, thereby eliminating the necessity of a separate mechanical load limiter. Thus, the present invention provides for manufacturing motorized seat belt retractors of a smaller size and at a low cost.
According to the present invention, the rotational resistance generating means of the motorized seat belt retractor generates a rotational resistance force by switching the motor into either the short circuited state or the non-short circuited state according to predetermined sequence control. According to this structure, a desired tensile load on the webbing can be obtained by suitably setting the period in which the motor is in the short circuited state and the period in which the motor is in the non-short circuited state and sequentially switching the short circuited state and the non-short circuited state of the motor.
In the motorized seat belt retractor, the non-short circuited state can mean that the motor is energized. According to this structure, the tensile load on the webbing can be controlled by utilizing the rotational torque of the motor. The rotational resistance force of the motor in the non-short circuited state (i.e., energized state) is adjustable, thereby allowing a wider range for the setting value of the tensile load on the webbing.
In the motorized seat belt retractor, the non-short circuited state can mean that the motor is electrically connected via a resistor. According to this structure, the rotational resistance force of the motor in the non-short circuited state can be adjusted by changing the resistance value of the resistor, thereby allowing a wider range for the setting value of the tensile load on the webbing.
In the motorized seat belt retractor, the non-short circuited state can mean that the motor is electrically open. According to this structure, little rotational resistance force is generated by the motor in the non-short circuited state when the motor is electrically disconnected (open-circuit), thereby easily allowing a wider range for the setting value of the tensile load on the webbing at a low cost without any complex mechanism.
The load limiter of the motorized seat belt retractor includes a gear train which couples the shaft of the motor to a spool on which the webbing is wound. According to this structure, the tensile load on the webbing can be controlled not only by adjusting the rotational resistance force of the motor but also by changing the gear ratio of the gear train.
In the aforementioned rotational resistance generating means which generates rotational resistance force by the motor, the rotational resistance force further acts for preventing a rotational shaft of a motor from rotating in a direction of withdrawing the webbing. According to this structure, the rotating shaft of the motor is electrically locked, thus preventing rotation of the shaft at a suitable timing.
According to the present invention, described in general above, it is preferred that the rotational resistance force be generated at least by counter-electromotive force generated by the rotation of the rotational shaft of the motor when short circuited. According to this structure, the counter-electromotive force generated by the rotation of the rotational shaft of the motor when short circuited can be utilized as the locking mechanism, thereby eliminating specific control for driving the motor.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.